On Wed, Apr 27, 2011 at 5:34 PM, KAMEZAWA Hiroyuki<kamezawa.hiroyu@jp.fujitsu.com> wrote:> On Wed, 27 Apr 2011 01:25:23 +0900> Minchan Kim <minchan.kim@gmail.com> wrote:>>> This patch defines new APIs to putback the page into previous position of LRU.>> The idea is simple.>>>> When we try to putback the page into lru list and if friends(prev, next) of the pages>> still is nearest neighbor, we can insert isolated page into prev's next instead of>> head of LRU list. So it keeps LRU history without losing the LRU information.>>>> Before :>> LRU POV : H - P1 - P2 - P3 - P4 -T>>>> Isolate P3 :>> LRU POV : H - P1 - P2 - P4 - T>>>> Putback P3 :>> if (P2->next == P4)>> putback(P3, P2);>> So,>> LRU POV : H - P1 - P2 - P3 - P4 -T>>>> For implement, we defines new structure pages_lru which remebers>> both lru friend pages of isolated one and handling functions.>>>> But this approach has a problem on contiguous pages.>> In this case, my idea can not work since friend pages are isolated, too.>> It means prev_page->next == next_page always is false and both pages are not>> LRU any more at that time. It's pointed out by Rik at LSF/MM summit.>> So for solving the problem, I can change the idea.>> I think we don't need both friend(prev, next) pages relation but>> just consider either prev or next page that it is still same LRU.>> Worset case in this approach, prev or next page is free and allocate new>> so it's in head of LRU and our isolated page is located on next of head.>> But it's almost same situation with current problem. So it doesn't make worse>> than now and it would be rare. But in this version, I implement based on idea>> discussed at LSF/MM. If my new idea makes sense, I will change it.>>>> I think using only 'next'(prev?) pointer will be enough.